1. Field of the Invention
The present invention relates to semiconductor manufacturing systems, and more particularly to a semiconductor manufacturing system for processing semiconductor wafers on a lot-by-lot basis, each lot including a plurality of semiconductor wafers.
2. Description of the Background Art
FIG. 11 is a schematic diagram showing the structure of a conventional semiconductor manufacturing line. Referring to FIG. 11, in the conventional semiconductor manufacturing line, processing apparatuses 1a to 1g, measuring apparatuses 2a to 2c, an inspecting apparatus 3a and storage equipment 4 are arranged separately. In the semiconductor manufacturing line, semiconductor wafers are normally subjected to the steps in processing apparatuses 1a to 1g. measuring apparatuses 2a to 2c, and inspecting apparatus 3a on a lot-by-lot basis, wherein about 24 semiconductor wafers form one lot 5. Each lot 5 is stored in storage equipment 4 while being not subjected to the steps in processing apparatuses 1a to 1g, measuring apparatuses 2a to 2c, and inspecting apparatus 3a.
FIG. 12 is a schematic diagram showing one example of a manufacturing flow of the conventional semiconductor manufacturing line. Referring to FIG. 12, in this manufacturing flow, lot 5 (see FIG. 11) is processed in processing apparatus 1a and then transported into storage equipment 4 for waiting. Thereafter, this lot 5 is processed in processing apparatus 1b, measured in measuring apparatus 2a and thereafter transported into storage equipment 4 for waiting. Thereafter, this lot 5 is processed in processing apparatus 1c and then transported again into storage equipment 4 for waiting. Thereafter, the lot 5 took out from storage equipment 4 is inspected in inspecting apparatus 3a. Thus, lot 5 is conventionally kept in storage equipment 4 while not being subjected to the steps in the processing apparatuses, the measuring apparatuses, and the inspecting apparatus.
FIG. 13 is a schematic diagram showing processing conditions of a conventional manufacturing flow for forming a general isolation oxide film. Referring to FIG. 13, in this manufacturing flow, an oxide film having a thickness of 200 .ANG. is first formed in accordance with a recipe (processing condition) 1. Then, the thickness of thus formed oxide film is measured on a condition 1 of recipe 1. Thereafter, a nitride film having a thickness of 1000 .ANG. is formed in accordance with recipe 1 and then the thickness of the nitride film is measured on a condition 2 of a recipe 2. Thereafter, a photolithography processing is carried out on condition 1 of recipe 1.
According to the conventional semiconductor manufacturing line, time necessary for actual manufacturing step accounts for 30% of the total manufacturing time of semiconductor devices, while time for lot 5 to be left in storage equipment 4 for 60%, as shown in FIG. 14, leading to the following problems.
Since a clean room for use in semiconductor manufacturing line requires significant cost for maintenance, unprocessed wafers must be completed with a reduced stay in the clean room. According to the conventional semiconductor manufacturing line, however, lot 5 is just kept in the storage equipment without being processed for 60% of the total time required for completion of semiconductor devices, as described above. Therefore, it is difficult to effectively reduce the total stay of the lot in the clean room, resulting in difficulty in reducing maintenance cost for the clean room.
The inspection and measurement steps are apparently essential for improvement in yield (the rate of acceptable products to the total products obtained) of devices. However, these steps are time-consuming as well as much waiting time in the storage equipment is required for the wafers as described above, and therefore, omission or reduction in the number of the inspection and measurement steps cannot be avoided at the time of actual mass production. Therefore, it is difficult to further improve the yield of devices. Meanwhile, if the inspection and measurement steps are to be provided to improve the yield of devices, time required for these steps must be reduced. This requires the highest-possible-speed image processing system and a robot to be provided in the inspecting apparatus for example, leading to increase in cost for the inspecting apparatus. Such increase in cost for the facility results in increase in price of semiconductor devices.
In addition, it is known that a large amount of contaminants such as by-product resulting from processing are attached to the front and rear surfaces, particularly to the rear surfaces of processed wafers. When the wafers are batch-processed by wet cleaning as pre-processing of the subsequent step in the manufacturing flow, the above-mentioned contaminants are transferred onto the surface of an adjacent wafer. The step of removing contaminants must be included in order to prevent such a state, but in the conventional example, the step of removing contaminants cannot help being omitted at the expense of yield of products so as to reduce the total manufacturing time, as described above. Consequently, it has been difficult to increase yield of products.